Yes, it is pretty awful and commends anyone that pushes through such hell.
I am not sure if anyone else has experience this, but when brushing my tongue during a fast I become nauseas to the point of throwing up. I usually stop myself before I throw up, but when I was feeling continually ill I ended up brushing the back of my tongue till the point that I did throw up. The episode was a mixture of relief and horror. The ill feeling would come back as soon as I laid down or within an hour of throwing up.